Non-uniform multi-beam satellite communications system and method

ABSTRACT

A satellite broadcast system and method, particularly useful for television signals, allows for local as well as nationwide broadcast service by allocating greater satellite resources to the more important local service areas. This is accomplished by broadcasting a non-uniform pattern of local service beams and designing the system to establish different service area priorities through factors such as the individual beam powers, sizes, roll-off characteristics and peak-to-edge power differentials. Frequency reuse is enhanced by permitting a certain degree of cross-beam interference, with lower levels of interference established for the more important service areas.

[0001] This application is a regular application of ProvisionalApplication Ser. No. 60/062,004 filed on Oct. 17, 1997.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to satellite communication systems andmethods, and more particularly to the broadcast of signals on a localarea basis with some of the signal frequency bands repeated fordifferent areas.

[0004] 2. Description of the Related Art

[0005] Cable television systems have been used to provide localtelevision service, with the programming content differing from oneservice area to the next, in addition to nation-wide programdistribution in which all areas receive the same national programming.While satellite broadcasting has also been successfully used fornation-wide broadcasts, local area service has proven more difficult toachieve because of interference between signals intended for differentservice areas that have different program content. In the past,satellite broadcasts have been limited to a generally uniform largeregional coverage, such as the entire United States, without theinclusion of local service broadcasts.

[0006] “Spot” broadcast beams, which are smaller than regional beams,have been used previously for non-television satellite broadcasting,such as telephone applications. Two types of spot beam broadcasts havebeen employed. In one, illustrated in FIG. 1, a desired region 10 suchas a country is covered by a uniform grid of evenly spaced spot beams 12having equal sizes and output power levels. To assure complete areacoverage, adjacent beam spots are overlapped. Different andnon-overlapping frequency bands are assigned to the signals within eachpair of adjacent beams to prevent cross-beam signal interference. In thesimplified illustration of FIG. 1, four different frequency bands areemployed (designated #1, #2, #3 and #4), with each beam separated fromthe next closest beam with the same frequency band by at least one otherbeam having a different frequency band.

[0007] The uniform spot beams 12 provide a complete coverage of thedesired larger regional area 10, without significant interferencebetween beams. However, a distinct disadvantage of this approach is thatthe satellite's resources are evenly divided among target areas of keyimportance, such as high density population centers, and target areas ofmuch lesser importance such as mountainous and other less developedareas. This can result in either an overly complex satellite system, ora system that does not provide adequate capacity to the most importanttarget areas.

[0008] A second approach has been to broadcast different beams havingsignals within a common frequency band to separate target areas that arespaced far enough apart from each other to avoid significant cross-beaminterference, thus allowing for a higher signal capacity to those,areasthat are covered. The different beams can be broadcast with differentoutput powers, thus providing the greatest capacity for the mostimportant target areas. However, the requirement that the beam targetareas be spaced well apart from each other can result, in an inadequateoverall coverage area, and the broadcast signals are limited to only asingle frequency band.

[0009] Other U.S. patents to Acampora, U.S. Pat. No. 4,315,262, and toAssai, U.S. Pat. No. 4,868,886, describe spot beam satellitearrangements for use with point-to-point communication such astelephony. Acampora describes scanning spot beams over differentparallel strip zones having similar traffic demands. Assai describes asystem that can provide either a global beam or simultaneous global andspot beams. Neither one appears to be applicable to a high speed digitalsystem which is required for digital television transmission to multiplepopulation centers of various size using nonuniform sized spot beams.

SUMMARY OF THE INVENTION

[0010] The present invention provides a new and improved, highlyefficient system and method for satellite broadcast of local televisionand other types of service, either independently or together with largerregional broadcasts. Both bandwidth efficiency and communications linkperformance are significantly improved, with interference levels reducedfor the most important service areas. It allows for a higher overallsystem throughput to a given geographic region, and is economicallyviable because of its increased capacity and accommodation ofmarketplace realities in those areas.

[0011] These advantages are achieved by broadcasting multiple spot beamsfrom a spacecraft, such as a satellite, to different target areas in anon-uniform beam pattern, and providing at least some of the beams withdifferent respective signal frequency bands. However, at least some ofthe beams have a common frequency band, and such beams are directed tonon-overlapping target area locations to avoid excessive interference.Priorities are established among different target areas by assigningdifferent sizes and powers to different beams, with the higher powerbeams accommodating larger signal capacity and also resulting in a lowerinterference level from other beams. The priorities among differenttarget areas can also be set by the selection of antenna reflector sizesto produce different roll-off characteristics for different beams, andby varying the illumination tapers of different antenna feed horns toestablish different peak-to-edge power differentials for differentbeams.

[0012] These and other features and advantages of the invention will beapparent to those skilled in the art from the following detaileddescription, taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1, discussed above, is a conceptual diagram of a priorregional satellite broadcast coverage with a uniform pattern ofoverlapping beams;

[0014]FIG. 2 is a graph illustrating possible interference between twoseparate beams carrying signals within a common frequency band;

[0015]FIG. 3 is a conceptual diagram of a non-uniform spot beam patternused to enhance broadcast efficiency in accordance with the invention;

[0016]FIGS. 4a, 4 b, 4 c and 4 d are diagrams of right and left handcircular polarized spot beam patterns for four different broadcastfrequency bands in accordance with the invention, while

[0017]FIG. 4e is a diagram of the overall beam coverage produced by thespot beam patterns of FIGS. 4a, 4 b, 4 c and 4 d, all superimposed on amap of the United States;

[0018]FIGS. 5a, 5 b, 5 c and 5 d are diagrams of antenna feed hornlayouts that can produce the spot beam patterns of FIGS. 4a, 4 b, 4 cand 4 d, respectively;

[0019]FIG. 6 is an elevation view of a satellite with different sizedantenna reflectors for generating different sized spot beams;

[0020]FIG. 7 is a simplified sectional view of one of the reflectorsshown in FIG. 6, together with feed horns having different sizes andillumination tapers to produce different beam characteristics;

[0021]FIG. 8 is a block diagram of satellite circuitry that can be usedto produce beams with different power levels from different antennas;and

[0022]FIGS. 9a and 9 b are frequency diagrams illustrating two possiblefrequency polarization-segmentation schemes that can be employed forfour antenna reflectors broadcasting two channels per reflector.

DETAILED DESCRIPTION OF THE INVENTION

[0023] A basic problem in providing local television service fromsatellite broadcasts is the possibility of interference betweendifferent beams that are directed to different service areas, but carrysignals within the same frequency band. This problem is illustrated inFIG. 2, which depicts the signal gain as a function of location alongthe earth's surface for two beams 14 a and 14 b (see looking down fromabove) that are nominally spaced apart from each other at the earth'ssurface. Assuming an equal gain for each beam, their respective gaincharacteristics 16 a and 16 b follow generally parabolic lobes,extending down to the first nulls before sidelobe energy is created,well below the levels of concern. However, the signal gain within theuseful portion of each beam as a practical matter must exceed a specificthreshold level, designated Th in the drawing. The generally circularbeam patterns 14 a and 14 b encompass the central portions of theoverall beams, where the signal gain equals or exceeds Th. Thus, eventhough the useful beam contours 14 a and 14 b are shown as beingseparated from each other, lower gain peripheral roll-off portions ofeach beam may overlap into the other beam's target area. This isillustrated as occurring at signal gain level I, at which a lower gainportion of each beam crosses over into the target area of the otherbeam.

[0024] The effect of increasing the signal gain (power) for one of thebeams, such as the right hand beam 14 b, is also illustrated in F,IG. 2.Assume for example that the peak power for the beam's original gaincharacteristic 16 b is 40 dBi, but that the signal gain is thenincreased to gain characteristic 16 c, with a peak gain of 43 dBi (whichdoubles its power). This increases the interference level of beam 14 bcrossing over into beam 14 a by ΔI, but does not increase theinterference level of beam 14 a crossing over into beam 14 b. Thus,increasing the carrier power C for the first beam degrades thecarrier-to-interference (C/I) level for the second beam, whose powerlevel remains constant but which suffers greater interference, butimproves the C/I ratio for the first beam whose power has been increasedbecause the interference it receives from the second beam remainsconstant.

[0025] Another important contributor to signal degradation is thermalnoise N. Increasing a beam's power also increases the C/N ratio, sincethe thermal noise remains constant. Thus, increasing the power of one ofthe beams increases both the C/I and C/N ratios for that beam, while C/Nfor the other beam remains the same but its C/I ratio goes down becauseof increased interference from the first beam.

[0026] For satellite signal transmissions that are performed digitally,such as digital television, reductions in the C/N and C/I ratios are notperceived as a gradual degradation in the signal quality. Rather,because the system is received above a given threshold, higher relativenoise and interference levels can increase the duration and frequency oftotal signal outages during rain, thunder storms or other bad weatherconditions. The problem is not one of signal quality, which is alwayshigh for a digital system when the signal is received, but of the numberand duration of outages. In the past this has been addressed by spacingbeams with different signals in the same frequency band so far apartthat there is essentially no overlap between the beams, even in theirperipheral areas.

[0027] The present invention takes a more flexible approach that allowsfor a much more efficient utilization of satellite capacity, and makespossible both high quality local and regional broadcast service. Ratherthan attempting to totally eliminate any degradation in signal qualityat all, a non-uniformity is introduced into factors such as the beamsizes, distribution and powers, cross-beam interference levels, roll-offcharacteristics and peak-to-edge power differentials to allow theservice to the most important areas to be optimized. While this caninvolve some sacrifice of service levels to marginal areas, the netresult is to provide a higher degree of service (including localservice) to a greater portion of the population. Efficiency is furtherimproved by providing a high degree of frequency reuse, in which thesame frequency bands can be used repeatedly for different local targetareas. For purposes of this application the term “frequency band” is notlimited to any particular governmentally pre-assigned frequency band,and refers more generally to any desired continuous frequency spectrum,not all of which must be occupied at any given time.

[0028] The non-uniform beam size and distribution aspects of theinvention are illustrated in FIG. 3, in which target areas for signalswithin four different frequency bands are again designated by numbers 1,2, 3 and 4. However, in contrast to the prior uniform pattern of FIG. 1,the invention concentrates the beams on the areas of highest population,with the highest density of local service areas generally having thehighest density of beams. The beam sizes are tailored to each servicearea, with the regions of highest population density generally assignedmore but smaller beams to allow for a greater number of different localservice areas with relatively high power levels for each local area.

[0029] The right hand side 18 of FIG. 3 illustrates a region of closelyspaced and high density population centers, with a separate localservice beam 20. for each local service area. Beams with differentfrequency bands can overlap in this region to assure that each localservice area is fully covered. Different beams can also vary in size,with the smaller beams generally serving local services areas withhigher population densities. As with the prior uniform beam patternillustrated in FIG. 1, beams which operate at the same frequency bandare preferably spaced apart from each other. However, they do not haveto be spaced so far apart that cross-beam interference is totallyeliminated. Rather, to increase the satellite's frequency reuse andbroadcast to a greater number of local service areas, some overlap of aperipheral portion of one beam into the intended target area for anotherbeam with the same frequency band is permissible. In this situation thebeam power for the target area having the higher priority, which willgenerally be the area with the larger number of customers, can be sethigher than the power level of the beam which it overlaps.

[0030] The left hand region 21 of FIG. 3 illustrates a possible beamdistribution for a region with fewer population centers that are morewidely spaced and have lower population densities. The beam sizes aregenerally large than in the higher density region 18, and there arefewer beams for the same area. Note, however, that the new system canaccommodate local variations within an overall region, such as thehigher population density center 22 at the upper left hand corner of thefigure, which is served by a greater density of beams having somewhatsmaller average sizes than for the remainder of the overall region 20.

[0031] Gaps can be left between the beam coverage areas, and no localservice provided at all, in a region 24 of low population densitywithout significant population centers. While the idea of leaving someregions without any local service at all may be counter-intuitive, theactual result is to provide high quality local service to a largemajority of the overall population because of the more efficient use ofthe satellite's resources, and is a great improvement over the priorinability to provide local satellite television service anywhere.

[0032]FIGS. 4a-4 d illustrate how local television service can beprovided to the United States through the reuse of four differentfrequency bands, while FIGS. 5a-5 d illustrate antenna feed horn layoutsthat can be used to produce the spot beam patterns of FIGS. 4a-4 d,respectively. Both left and right hand circular polarization patternsare shown, and indicated respectively by dashed and solid lines. FIG. 4aillustrates seven beam target areas 26 a, all with the same frequencyband and distributed over different portions of the country, while FIG.5a illustrates a pattern of feed horns 27 a that can be used to producethe desired beam pattern from an antenna. Some cross-beam interferencecan be expected between such areas, as explained previously. Therelative beam powers are designed to produce an optimum tradeoff betweenthe number and durations of outages and the number of customers servedin each area.

[0033] Target areas for the three other frequency bands, designated 26b, 26 c and 26 d in FIGS. 4b, 4 c and 4 d, respectively, are assigned ina similar manner, with corresponding patterns of feed horns 27 b, 27 cand 27 d shown respectively in FIGS. 5b, 5 c and 5 d. The cumulativebeam pattern produced on the ground by all four sets of beam targetareas is illustrated in FIG. 4e. The target area for one frequency bandcan overlap with target areas for one or more different frequency bands;a target area for one band can encompass one or more smaller areas ofdifferent bands, or can be included within a larger area of a differentband. Cross-beam interference is not a concern in this case because thedifferent frequency bands do not overlap.

[0034] The beams illustrated in FIG. 4e all have circularcross-sections. While this would be most typical, shaped beams can alsobe produced by using a shaped antenna reflector on the satellite with asingle antenna feed horn, or less desirably by providing the same signalto multiple feed horns for the same reflector with proper amplitude andphase relationships to achieve the desired shape. Shaped beams may beuseful in ertain situations, such as broadcasting to a non-circulartarget area that is quite distant from the other beams. For example,Hawaii and Alaska could be good candidates for elliptical beams.

[0035]FIG. 6 illustrates in simplified form a satellite 28 with an arrayof antennas designed to implement the invention. The satellite is showncarrying four different broadcast antenna reflectors 30 a, 30 b, 30 cand 30 d, with solar cells mounted on panels 32 a and 32 b providing apower supply for the system. Reflectors 30 a and 30 b are larger thanreflectors 30 c and 30 d and, with appropriate feed horns, can producethe beam distributions shown in FIGS. 4b and 4 c, respectively; withappropriate feed horns reflectors 30 c and 30 d can produce the beamdistributions respectively shown in FIGS. 4a and 4 d.

[0036]FIG. 7 gives a simplified view of a reflector 34 which reflectsfeed beams from a number of feed horns 36 a, 36 b and 36 c; all of thefeed horns for a single reflector would normally be operated within thesame frequency band for a given signal polarization. The size of eachbeam is primarily a function of the reflector and horn dimensions, whilethe beam direction is a function of the reflector orientation relativeto ground and the feed horn orientations relative to the reflector.However, given a fixed common reflector size for several feed horns,differences in horn sizes can be used to produce spot beams which havecorresponding differences in size. Once a particular pattern of beamsizes and spatial distribution has been established, a specificreflector and feed horn design to implement the pattern involves merelyan application of conventional antenna design principals.

[0037] The size of each reflector also determines the roll-offcharacteristics of its beams, which is an important factor indeter-mining the C/I ratio for beams broadcast with the same frequencyband. In general, larger reflectors will produce better roll-offcharacteristics but will not be as easy to fit on the satellite, whereassmaller reflectors allow for a greater total number of reflectors for agiven satellite and a potentially closer spacing between beams with thesame frequency band, but will produce a degraded roll-off for a givenfeed horn type. The use of different size reflectors as illustrated inFIG. 6 thus results in different beams having different roll-offcharacteristics and adds another variable to the tradeoffs involved inproviding the highest quality service to the greatest number ofcustomers. In general, larger reflectors can be assigned to the moreimportant local service areas to provide better beam roll-offcharacteristics in those areas.

[0038] The use of different feed horn sizes to produce different beamsizes from the same reflector is illustrated by feed horns 36 a and 36b, which have different schematic representations. Because of theirdifferent positions relative to the reflector 34, feed horns 36 a and 36b will also result in beams that are directed to different local targetareas.

[0039] Another factor that affects service quality is the beam'speak-to-edge gain differential between the center and edge of theservice area. The smaller the differential, the higher will be thesignal quality towards the edges of the service area, but the overallpower consumption will also increase. On the other hand, a higherdifferential means that the beam power is falling more rapidly at theedge of its target area, and is thus less likely to interfere withnearby beams. This is another way in which the different service areascan be prioritize, with the more important areas served by feed hornswith illumination tapers that produce the lowest peak-to-edge gaindifferentials.

[0040] Another reason for assigning higher power levels to the beamsthat are broadcast to the more important service areas is that it allowsfor a larger number of station signals to be included within thefrequency bands broadcast to those areas. To the first order, increasingthe number of station signals reduces the power per signal, thusincreasing both relative thermal noise and cross-beam interferencelevels; an increase in total beam power can be used to compensate forthese signal degradations.

[0041]FIG. 8 illustrates the satellite circuitry used to generate thedifferent beams, with the circuitry for two channels 38 a and 38 bshown. Channel 38 a receives a ground signal via uplink antenna 40 a.The signal is delivered to a receiver 44 a, which includes a low noiseamplifier and a frequency converter that converts the uplink frequencyband UL1 to a desired downlink frequency band DL1. An input channelfilter 46 a passes the desired channel, rejecting other channels. Theresulting downlink channel signal is routed through an automatic levelcontrol (ALC) pre-amplifier 48 a and a high power non-linear amplifier(typically a traveling wave tube or a solid state device) 50 a. Theamplified output is filtered by an output channel filter 52 a, whichpasses the amplified channel band and blocks other unwanted frequencies,and then delivered to the feed horn of a downlink antenna 54 a. Power issupplied to the channel circuitry from an on-board power supply 56,conventionally solar cells on the satellite panels 32 a and 32 billustrated in FIG. 6.

[0042] The second channel has a similar configuration, with its ownuplink antenna 40 b, receiver 44 b which performs an uplink(UL2)-to-downlink (DL2) frequency conversion, input channel filter 46 bwhich passes the desired second channel and rejects other channels, ALC48 b, power amplifier 50 b, output channel filter 52 b which passes theamplified channel downlink frequency band and rejects other channels,and another antenna feed horn 54 b. To reduce the total number of poweramplifiers required, the signals for multiple lower power beams can beprocessed by a common power amplifier as described in U.S. patentapplication Ser. No. 60/062,005, filed on the same day as thisapplication by John L. Norin and entitled “Method and Apparatus forSpacecraft Amplification of Multi-Channel Signals”, the contents ofwhich application is incorporated herein by reference. To compensate forvariances between actual and designed beam power profiles, changes inthe relative importance of different service areas over time, andchanges in the number of station signals broadcast to a given targetarea, the amplifier drives can be adjusted from the ground as describedin U.S. patent application Ser. No. 60/062,003 filed on the same day asthis application by John L. Norin and entitled “Dynamic InterferenceOptimization Method for Satellites Transmitting Multiple Beams With aCommon Frequency Channel”, the contents of -which application are alsoincorporated herein by reference.

[0043] Assuming that channel 38 a is allocated to a more important localservice area than channel 38 b, its high power amplifier 50 a willnormally be selected to produce a greater power output than amplifier 50b in channel 38 b. This is indicated in FIG. 8 by a larger amplifiersymbol for 50 a than for 50 b.

[0044] At present, 32 transponder channels are typical for satellitetelevision broadcasts in a given service, representing 16 differentchannels 24 MHz wide and separated by approximately 5 MHz, and twoorthogonal polarizations (either left and right hand circular orvertical and horizontal) for each frequency band. In the preferredsystem the majority of the available channels are used for nationwidebroadcasts, with the remaining channels reserved for local servicebeams. FIGS. 9a and 9 b illustrate two possible schemes for dividingeight channels among four different reflectors, with the four differentfrequency bands indicated respectively by S1, S2, S3 and S4. In FIG. 9aeach reflector broadcasts two signals of opposite polarization (POL1 andPOL2) but within the same frequency band. In FIG. 9b each reflectorbroadcasts a signal within one frequency band at the first polarization,and another signal within a different frequency band at the secondpolarization.

[0045] While all of the beams would typically be broadcast from a singlesatellite,, situations may arise that could lead to a distribution ofthe beams among multiple satellites. For example, where the desired feedsize does not allow adjacent beams to use the same reflector surface tofeed packaging interference, the greater antenna-to-antenna andsatellite-to-satellite pointing differences normally associated with amultiple satellite system might be justified.

[0046] While particular embodiments of the invention have been shown anddescribed, numerous variations and alternate embodiments will occur tothose skilled in the art. Accordingly, it is intended that the inventionbe limited only in terms of the appended claims.

We claim:
 1. A spacecraft broadcast method, comprising: broadcastingmultiple communication signal beams from a spacecraft to differentrespective target area locations in a non-uniform beam pattern, andproviding different respective signal frequency spectrums for at leastsome of said beams.
 2. The method of claim 1 , wherein at least some ofsaid beams have a common signal frequency spectrum, and all of the beamswith the same common frequency spectrum are directed to non-overlappingtarget area locations.
 3. The method of claim 1 , wherein at least someof said beams have different sizes at their respective target arealocations.
 4. The method of claim 1 , wherein at least some of saidbeams are broadcast to produce different beam powers at their respectivetarget area locations.
 5. The method of claim 4 , wherein said at leastsome beams are broadcast from the spacecraft with different respectivebeam powers.
 6. The method of claim 1 , wherein at least some of saidbeams with different signal frequency spectrums are broadcast tooverlapping target area locations.
 7. The method of claim 1 , wherein atleast some of said beams are broadcast with different respective signalbandwidths.
 8. The method of claim 1 , wherein at least some of saidbeams are broadcast with different beam roll-off characteristics.
 9. Themethod of claim 1 , wherein at least some of said beams are broadcastwith different peak-to-edge power differentials.
 10. A spacecraftbroadcast method, comprising: broadcasting multiple communication signalbeams from a spacecraft to different respective target area locations sothat at least some of said beams have different sizes at theirrespective target locations, and providing different respective signalfrequency spectrums for at least some of said beams.
 11. The method ofclaim 10 , wherein at least some of said beams have a common signalfrequency spectrum, and all of the beams with the same common frequencyspectrum are directed to non-overlapping target locations.
 12. Themethod of claim 10 , wherein at least some of said beams are broadcastto produce different beam powers at their respective target arealocations.
 13. The method of claim 12 , wherein said at least some beamsare braodcast from the spacecraft with different respective beam powers.14. The method of claim 10 , wherein at least some of said beams withdifferent signal frequency spectrums are broadcast to overlapping targetarea locations.
 15. The method of claim 10 , wherein at least some ofsaid beams are broadcast with different respective signal bandwidths.16. The method of claim 10 , wherein at least some of said beams arebroadcast with different beam roll-off characteristics.
 17. The methodof claim 10 , wherein at least some of said beams are broadcast withdifferent peak-to-edge power differentials.
 18. A spacecraft broadcastmethod, comprising: broadcasting multiple communication signal beamsfrom a spacecraft to different respective target area locations with atleast some of said beams having different beam powers at theirrespective target area locations, and providing different respectivesignal frequency spectrums for at least some of said beams.
 19. Themethod of claim 18 , wherein said at least some beams are broadcast fromthe spacecraft with different respective beam powers.
 20. The method ofclaim 18 , wherein at least some of said beams have a common signalfrequency spectrum, and all of the beams with the same common frequencyspectrum are directed to non-overlapping target area locations.
 21. Themethod of claim 18 , wherein at least some of said beams with differentfrequency bands are broadcast to overlapping target area locations. 22.The method of claim 18 , wherein at least some of said beams arebroadcast with different respective signal bandwidths.
 23. The method ofclaim 18 , wherein at least some of said beams are broadcast withdifferent beam roll-off characteristics.
 24. The method of claim 18 ,wherein at least some of said beams are broadcast with differentpeak-to-edge power differentials.
 25. A spacecraft broadcast method,comprising: broadcasting multiple communication signal beams from aspacecraft to respective non-overlapping target area locations so thatat least some of said beams have different sizes at their respectivetarget area locations, and providing a common signal frequency spectrumfor each of said beams.
 26. The method of claim 25 , wherein at leastsome of said beams are broadcast to produce different beam powers attheir respective target area locations.
 27. The method of claim 26 ,wherein said at least some beams are broadcast from the spacecraft withdifferent respective beam powers.
 28. The method of claim 25 , whereinat least some of said beams are broadcast with different respectivesignal bandwidths.
 29. The method of claim 25 , wherein at least some ofsaid beams are broadcast with different beam roll-off characteristics.30. The method of claim 25 , wherein at least some of said beams arebroadcast with different peak-to-edge power differentials.
 31. Aspacecraft antenna array for multi-beam broadcasts to earth, comprising:a plurality of antenna reflectors, and at least one respective feed hornassociated with each reflector, said antenna reflectors and theirrespective feed horns configured to broadcast a plurality ofcommunication signal beams in a non-uniform beam pattern with at leastsome of said beams having different sizes.
 32. The spacecraft antennaarray of claim 31 , at least some of said reflectors having differentsizes to produce respective beams with different roll-offcharacteristics.
 33. The spacecraft antenna array of claim 31 , at leastsome of said feed horns having different respective illumination tapersto produce respective beams with different peak-to-edge powerdifferentials.
 34. A spacecraft broadcast system for multi-beambroadcasts to earth, comprising: a spacecraft, a plurality of antennareflectors with respective feed horns carried by said spacecraft, and apower supply and radio frequency (RF) signal circuitry carried by saidspacecraft for energizing said feed horns to broadcast respectivecommunication signal beams to respective target area locations on earthvia their respective reflectors, said antenna reflectors and theirrespective feed horns configured to broadcast said beams in anon-uniform beam pattern with at least some of said beams havingdifferent sizes.
 35. The spacecraft broadcast system of claim 34 ,wherein said power supply and RF signal circuitry energize said feedhorns to broadcast at least some of said beams within differentrespective signal frequency spectrums.
 36. The spacecraft broadcastsystem of claim 35 , wherein said power supply and RF signal circuitryenergize said feed horns to broadcast at least some of said beams toproduce different respective beam powers at their respective target arealocations.
 37. The spacecraft broadcast system of claim 35 , whereinsaid reflectors and feed horns are configured to broadcast at least someof said beams with different signal frequency spectrums to overlappingtarget area locations.
 38. The spacecraft broadcast system of claim 35 ,wherein said power supply and RF signal circuitry energize at least twoof said beams with a common frequency spectrum.
 39. The spacecraftbroadcast system of claim 38 , wherein said reflectors and feed hornsare configured to broadcast said common frequency spectrum beams tonon-overlapping target area locations.
 40. The spacecraft broadcastsystem of claim 34 , wherein said power supply and RF signal circuitryenergize said feed horns to broadcast at least some of said beams toproduce different respective beam powers at their respective targetlocations.
 41. The spacecraft broadcast system of claim 40 , whereinsaid power supply and RF signal circuitry energize said feed horns tobroadcast said at least some beams from the spacecraft with differentrespective beam powers.
 42. The spacecraft broadcast system of claim 34, wherein said power supply and RF signal circuitry energize at leasttwo of said beams with a common signal frequency spectrum.
 43. Thespacecraft broadcast system of claim 42 , wherein said reflectors andfeed horns are configured to broadcast said common frequency spectrumbeams to non-overlapping target area locations.
 44. The spacecraftbroadcast system of claim 34 , at least some of said reflectors havingdifferent sizes to produce respective beams with different roll-offcharacteristics.
 45. The spacecraft broadcast system of claim 34 , atleast some of said feed horns having different respective illuminationtapers to produce respective beams with different peak-to-edge powerdifferentials.